A silica-loaded catalyst which is used for producing a corresponding unsaturated nitrile by a vapor-phase catalytic ammoxidation reaction of propane or isobutane. The silica-loaded catalyst contains a metal oxide represented by formula (1) and has an average pore diameter of 60-120 nm, a total pore volume of 0.15 cm3/g or more, a specific surface area of 5-25 m2/g, and a crystallite size of 40-250 nm as calculated using the half width of the (001) peak as determined by X-ray diffraction. MoVaNbbXcTdZeOn (1) (In formula (1), X represents at least one element selected from among Sb and Te; T represents at least one element selected from among Ti, W, Mn and Bi; Z represents at least one element selected from among La, Ce, Yb and Y; and a, b, c, d and e are respectively within the following ranges, 0.05<=a<=0.5, 0.01<=b<=0.5, 0.001<=c<=0.5, 0<=d<=1 and 0<=e<=1, and n represents a number that maintains a balance among the atomic valences.)